How to make such a strange file has no active object?
How to make the scene without any active object.

Since the issue is solved, I will explain by myself. 
Consider the case where are two objects "Cube" and "Cone" exist. 
"Cube" is selected and on the first layer. But the layer is turned off. On the other hand, "Cone" is active and on the second layer turnd on. 
When "Cone" is deleted, active object will be None. However, "cube" is still selected. 
If you turn on the second layer, the scene is completed.